The large-scale, economic purification of proteins is required for viable biotechnology products. Generally, proteins are produced by cell culture, using either mammalian or bacterial cell lines engineered to produce the protein of interest by insertion of a recombinant plasmid containing the gene for that protein. Since the cell lines used are living organisms, they must be fed with a complex growth medium which usually contains a mixture of salts, sugars, amino acids, vitamins, trace elements and peptones. Separation of the desired protein from the mixture of compounds fed to the cells and from the by-products of the cells themselves to a purity sufficient for use as a human therapeutic poses a formidable challenge.
Recombinant therapeutic proteins are commonly produced in several host cell lines including mammalian host cells, such as, for example, murine myeloma NS0 and Chinese Hamster Ovary (CHO) cells (Anderson, D. C and Krummen, L. (2002) Curr. Opin. Biotech. 13: 117-123; Chu, L. and Robinson, D. K. (2001) Curr. Opin. Biotechnol. 12:180-187) and bacterial host cells including Escherichia coli (E. coli). Each cell line has advantages and disadvantages in terms of productivity and the characteristics of the proteins produced by the cells. Escherichia coli has been most extensively used for the large-scale production of therapeutic proteins, which do not require complex glycosylation for bioactivity. Heterologous proteins expressed by E. coli may accumulate as soluble product or insoluble aggregates. Generally, to isolate the proteins, the cells may be subjected to treatments for periplasmic extraction or be lysed to release intracellular products that are otherwise inaccessible. Advances in fermentation and cell culture techniques have greatly increased the titers of targeted recombinant proteins.
Choices of commercial production cell lines often balance the need for high productivity with the ability to deliver the product quality attributes required of a given product. Under cGMP fermentation procedures, quality is built into the entire process ensuring that regulatory agencies requirements are met in terms of safety, product identity, quality and purity. However, occasionally issues arise in which a given product does not meet its specifications. The challenge is to develop a robust process in which to identify and isolate the issue, then mitigate the issue such that process controls can be maintained within established parameter ranges, and make sure the process consistently produces a product that meets product specifications. There is a need in the art for mitigating or eliminating the incidence of products that do not meet specifications.